(1) Field of the Invention
The present invention relates to a dielectric multi-line resonator, including a coaxial resonator providing a one-fourth wavelength line having one end opened and the other end shorted through a dielectric material block surrounded by an earthed conductor, which is used principally for UHF band, particularly for remarkably reducing the variation of resonant frequency in comparison with the conventional one, which is caused by external connection.
(2) Description of the Prior Art
For coupling a coaxial resonator, which is basically formed by providing a one-fourth wavelength line having one end opened and the other end shorted through a dielectric material block surrounded by an earthed conductor, with an external circuit, a capacitive coupling means has been almost exclusively employed mainly by reason of the readiness of composition and manufacture. Concretely speaking, as shown in FIG. 1A, in a typical coaxial resonator formed of an inside wall face conductor 4 of a central hole 3 provided through a dielectric material block 2 of one-fourth wavelength height, which is surrounded by side face conductors 1a and a bottom face conductor 1b, a terminal conductor 6 supported by an insulator 5 is inserted into the upper end portion of the central hole 3, and hence the external terminal coupling is attained by the capacity between the side face conductor 4 operated as the resonant line and the terminal conductor 6. In the other case, as shown in FIG. 1B, in the coaxial resonator arranged the same as described above, another terminal conductor 8 is inserted into a small hole 7 provided in the upper end portion of the dielectric material block 2 close by the side face conductor 4, and hence the external terminal coupling is attained by the capacity between both of those conductors 4 and 8.
However, the above mentioned capacitive external coupling to the coaxial resonator has a difficulty such that the variation of resonant frequency in response to the extent of coupling to external circuits is extensive, and further precise manufacturing is required by the dependency of the coupling extent on shape and size, in spite of the advantage that the structure is simple, with resulting facilitated manufacturing and further stable coupling can be attained.
On the other hand, with regard to the resonant frequency variation responding to the coupling extent, the inductive coupling based on coils or the like is more tolerant and hence the coupling to external circuits can be stabilized thereby. However, the conventional structure thereof has difficulties such that the manufacturing takes much time and much labor and hence is not suited for mass-production.